The invention concerns a gemstone having a faceted crown which is inclined with respect to the main axis and which is defined on the one hand by a preferably flat table and on the other hand by a peripheral edge of the gemstone. A faceted pavilion is inclined with respect to the main axis and adjoins the peripheral edge and converges to a tip.
In the case of artificial gemstones, in particular glass gemstones, there is from time to time an interest in achieving a reflection characteristic which radiates in as wide spread a fashion as possible, when there is central illumination on to the table.
In order to achieve that, the invention proposes that the facets of the crown are all inclined at the same crown angle with respect to the main axis while the facets of the pavilion are inclined at two different pavilion angles with respect to the main axis. The first set of facets of the pavilion are inclined at a first pavilion angle and extend to the peripheral edge, and the second set of facets of the pavilion are inclined at a second pavilion angle and start from the tip without reaching the peripheral edge.
The Applicants"" measurements have shown that a widening of the reflection characteristics can be achieved by cutting a second pavilion angle, that is to say a second set of facets, which are inclined at a shallower angle with respect to the main axis. Upon central illumination in the direction of the main axis on to the table, therefore, relevant levels of radiation intensity are still to be expected even at relatively large angles with respect to the main axis.
It has proven to be particularly advantageous if the second set of facets of the pavilion which are inclined at the second pavilion angle, in a view from below directed on to the tip of the gemstone, extend radially over a distance of between 25% and 75% of the projected tip-peripheral edge spacing (grinding depth of the second layer of between 25% and 75%).
A further alternative configuration of the invention is characterized in that the facets of the crown are all inclined at the same crown angle with respect to the main axis while the facets of the pavilion are inclined at two different pavilion angles with respect to the main axis. The first set of facets of the pavilion are inclined at a first pavilion angle and extend to the peripheral edge, and the second set of facets of the pavilion are inclined at a second pavilion angle and start from the tip. The crown angle is between 40xc2x0 and 44xc2x0 (preferably about 42xc2x0), the first pavilion angle is between 40xc2x0 and 44xc2x0 (preferably about 42xc2x0), and the second pavilion angle is between 32xc2x0 and 36xc2x0 (preferably about 34xc2x0).